Most electronic converters for converting AC power main voltage to a voltage for driving a lamp, such as a halogen lamp, are based on self-oscillating technology using bipolar transistors. Since bipolar transistors are current operating devices, obtaining feedback for oscillation is relatively simple. However, bipolar transistor converters with or without diode rectification suffer from several disadvantages. For example they are subject to secondary breakdown phenomena, increased current leakage and increased power losses at elevated temperatures. The practical limit for junction temperature is 100° C. (case temperature typically 85° C.). Bipolar transistor converters are also expensive for high voltage applications (for example 277V, 240V and 220V). They also are less efficient in operation than field-effect transistors, because a typical limitation on frequency of operation is 35 kHz due to switching losses. Precise protection against fault conditions is difficult in a simple circuit using bipolar transistors. In addition, size reduction is limited due to operating frequency limitations, and it is difficult to achieve UL Class B temperature classification (130° C. maximum insulation limitation) without a sacrifice in reliability.
U.S. Pat. No. 6,157,551 to Barak, et al., assigned to Lightech Electronic Industries Ltd., which issued Dec. 5, 2000, teaches a power converter using bipolar transistors. However, this converter suffers from the foregoing disadvantages.
U.S. Pat. No. 6,208,806 to Nerone, assigned to General Electric, which issued Mar. 21, 2001, teaches a power converter using N-channel and P-channel field effect transistors (FETs). Nerone achieves size reduction and improves efficiency by operating at higher frequencies (30 kHz-90 kHz). However, Nerone fails to address the issue of high temperature operation and fault protection. Besides, P-channel FETs are expensive and difficult to obtain compared to N-channel FETs.
There therefore exists a need for a converter that is simple and inexpensive to construct, while providing fault protection and achieving reliable, sustained operation at elevated operating temperatures.